光学频率梳（光频梳）是一系列等间隔分布、高相干的光学纵模构成的宽光谱光源，这使其区别于其它传统激光光源，实现了诸多光学计量应用重大突破。分辨并充分利用离散纵模的信息是光频梳应用中的一大难点。双光梳系统能有效地解决这个问题，从而成为一种新型的光学测量工具。它利用两台具有微小重频差的相干光频梳将光谱信息通过梳齿一一对应的多外差干涉方式映射至射频域，其测量过程不再受传统光谱仪响应带宽、分辨力等因素的限制，实现了高分辨力、高灵敏度的宽带光学信息快速测量。通过提取信号的幅频信息和相频信息，双光梳系统在光谱测量、绝对距离测量及相关延伸领域中得到了广泛应用。首先，实现高精度双光梳系统需要分析解决光源的噪声问题。本论文详细分析了双光梳系统中噪声的来源及其影响，提出了双光梳系统噪声模型。并研究了同步锁定和数字补偿两种有效方式进行噪声抑制或补偿，实现了纵模可分辨、相位稳定的双光梳系统，为高精度双光梳应用打下了基础。其次，本论文基于上述高精度双光梳系统的相频信息提出双光梳组合方法绝对距离测量系统。我们将三种传统的测距方法——飞行时间法、合成波法、载波干涉法融合到双光梳测距系统中，在保障测距范围（~2.67米）和测距精度（~8纳米）的同时，利用合成波法实现了飞行时间法到载波干涉法的快速（~5毫秒）准确衔接。文中还进行了双光梳测距结果的不确定度分析，给出了优化系统参数的理论指导。并表明空气折射率的不确定度是限制几何距离准确性的关键因素。不同于依赖空气参数测量确定空气折射率的经验公式法，本文首次将双色法应用到双光梳系统中，实现全路径空气折射率校正，直接获得不确定度为~10?7的几何距离值。最后，论文还利用上述高精度双光梳系统的幅频信息进行光纤光栅传感器的光谱响应测量，该系统适用于温度变化环境中的应变传感。系统应变测量的精度达到0.5微应变，可以实现频率为百赫兹及以下的应变传感，动态分辨力达到1.5微应变。文章详细分析了包括光源相位噪声、探测器噪声、光纤光栅带宽等对应变分辨力的影响。通过仿真验证了本文的高精度双光梳系统可以实现的理论应力分辨力约为10纳应变。
Optical frequency combs (OFCs) are broadband light source consisting of an array of phase-coherent spectral lines that are evenly spaced in frequency domain, which makes it distinguished with conventional laser souces and achieve breakthrough in optical metrology field. Resolving and utilizing the discrete comb modes’ information becomes a difficulty in OFCs’ applications. The dual-comb system (DCS) is such a novel optical measurement instrument that employs two coherent OFCs with slight repetition rate difference, and it effectively maps optical spectra to radio frequency domain on a comb tooth-by-tooth multi-heterodyne basis. This process gets rid of conventional spectrometers’ response and resolution limitations, and realizes fast broadband optical response measurement with high resolution and high sensivity. DCS has been widely applied in spectroscopy, ranging and extended fields by extract amplitude and phase information of an OFC. At first, analysis and solutions concerned to OFCs’ phase noise are necessary for realizing a precise DCS. The thesis gives a DCS’s noise model after analyzing the origin and impact of noise. Then two effective noise suppression methods are proposed to realize a mode-resolved and phase-stable DCS, which is the basis for precise dual-comb applications.Then, the thesis proposes a dual-comb combined-method ranging system based on the precise DCS. We combine three conventional ranging methods: time-of-flight (TOF) method, synthetic wavelength interferometry (SWI), and carrier wavelength interferometry (CWI) in the ranging system. The TOF method provides large range (~2.67 m), the CWI provides high precision (~8 nm) and the SWI provides accurate and rapid (~5 ms) link between TOF method and CWI. We also analyze the uncertainty of the dual-comb ranging system and give a theory of optimization of system’s parmameters. Furthermore, the refractive index of air becomes key factor that limits the accuracy of the ranging system. Different with the conventional method that compensate refractive index of air using empirical equations by monitoring environment parameters, the thesis first applies the two-color method to the dual-comb ranging system. We realize all-path correction of refractive index of air and achieve an accuracy of the order of ~10?7.Finally, we utilize amplitude infomations of the precise DCS to measure spectral response of a fiber bragg grating (FBG) sensor. The system is applied to strain sensing under circumstance with unstable temperature. The precision of the system reaches 0.5 microstrain, and realize measurement of ~100 Hz range strain signal. The dynamic resolution reaches ~1.5 microstrain. We detailedly analyze the factors affect the strain resolution, including phase noise of light source, noise of photodetector, and bandwidth of the FBG. The simulation results demonstrate a theoretical strain resolution of the precise DCS reaches ~10 nanostrain.
